What does the push button do?

MM

I believe you hold the switch down when you arm the system to stop the sparking happening at the connection.
Not needed on 4 cells as they only put out a small spark.

(The sparking causes pitting and therefore a bad connection.)

This looks like a solid, good system.
I however, prefer a more minimalist approach.
9 years ago I started out with Deans, but I liked 4 mm bullet connectors better, also over other dual contact types.

I'm adding just one item in the chain, the spark suppressor...

Made from a male & female bullet connector, a piece of hex brass rod, a resistor and some shrink tubing.
Drill the hex brass bit with 4mm length wise. Cut off a piece about 8 mm long.
Solder both connectors in series (I'm using a tiny bit of heavy, solid copper wire), cover the female part in shrink tubing.
Measure the OD of that part and drill with that diameter into the hex brass rod until just a few mm of 4mm diam. stands left.
Solder one end of the resistor to the outside of the brass.
Push the female end all the way into the hex bit, solder the other end of the resistor to the male bit , cover the whole unit in shrink tubing and you're done. I'm leaving the suppressor on the ESC lead and plug in the battery.
Because this connection is outside the fuselage, I also don't need another arming plug. Too many chances of something going wrong.
Flight tested this outfit over quite some years now and I can say I'm happy with it.




In action:

And then we can have two buttons to push to fly. Cool.